per the uniden owner's manual page 27
"If this is the first time you have turned on the scanner, All LocOut displays. This means that no frequencies have been saved into channels. Press Srch to beginsearching."
The simplest way for this to occur is that you have just locked out all your programmed frequencies. Just manually step to any channel in a bank that is toggled on and has programming in it, and toggle the LO key to reestablish at least one channel to be unlocked.
Tip: if you have accidentally locked out all channels in a bank, and just want them all to be unlocked, you can hold down the LO key for 3 or more seconds and the whole bank will be unlocked without having to step through them.
Another way for this to occur is if you toggle on a bank that has no programming in it (all zeros - anything all zeros is locked out automatically), AND have toggled OFF all banks that DO have programming in it.
Of course if you haven't done any programming at all, you are limited only to searching, and not scanning.